I heard that in Crown Heights they don’t start dating until they confirm that their numbers match up, though I cannot confirm this to be actual practice.
I know that this is tabu by the general public, like
BP, flatbush, Monsey, Lakewood, especially the Heimishe yidden.
I wonder why though? Doesn’t it make sense to avoid any hardships that will arise when they really like each only to find out they are not compatible.